1. Field of the Invention
The present invention relates to a boundary acoustic wave device utilizing boundary acoustic waves propagating at a boundary between a piezoelectric substance and a dielectric substance and a method for manufacturing the same. More specifically, the present invention relates to a boundary acoustic wave device including an electrode film disposed between a piezoelectric substance and a dielectric substance, the electrode film being made of an Au alloy, and a method for manufacturing the same.
2. Description of the Related Art
Boundary acoustic wave devices have been used as resonators and band-pass filters. A boundary acoustic wave device includes an IDT electrode that is disposed at a boundary between a first medium and a second medium. The boundary acoustic wave device uses boundary acoustic waves propagating along the boundary. Therefore, the boundary acoustic wave device can be mechanically supported on a surface opposite to the boundary between the first and second media. Therefore, a package structure can be simplified and miniaturized.
An example of such a boundary acoustic wave device is disclosed in WO2004/070946. WO2004/070946 discloses that an IDT electrode is configured using Au, Ag, Cu, or Al, or an alloy thereof. WO2004/070946 also describes that in order to enhance electric power resistance, a second electrode layer made of a metallic material such as Ti, Cr, or NiCr may be laminated on at least one of the surfaces of an electrode layer made of Au, Ag, Cu, or Al, or an alloy thereof. However, WO2004/070946 only shows in specific examples IDT electrodes that include an electrode layer made of Au and Ti layers provided above and below the electrode layer, but no specific examples using other materials.
In a boundary acoustic wave device, acoustic waves propagate not only in a piezoelectric substance but also in the IDT disposed at a boundary between a piezoelectric substance and a dielectric layer. Therefore, a large stress is applied to an IDT electrode. Thus, a boundary acoustic wave device has a problem of low electric power resistance as compared to surface acoustic wave devices.
WO2004/070946 discloses that in the boundary acoustic wave device, the electric power resistance is enhanced by laminating the Ti layers above and below the electrode layer made of Au.
However, the structure in which the Ti layers are laminated above and below the electrode layer made of Au does not have sufficient electric power resistance, and further improvements in the electric power resistance have been required.
Furthermore, in a boundary acoustic wave device, there has been an unmet significant demand for not only enhancing electric power resistance but also decreasing insertion loss.